If there’s one subject I tend to get preachy about, it’s sleep. It’s not exciting like a new exercise protocol or as sexy as some new diet trend, so it doesn’t get the coverage it deserves. But it is absolutely crucial that you get a full night of sleep. This is probably going to turn into a 3-4 post series, so I want to start off with something tangible that we can really sink our teeth into to get the ball rolling.

Today we’re talking about how sleep can help make you sexy. Putting aside the considerable health implications of neglecting sleep, we’re starting off on a topic more immediately relevant to most of you – body composition – losing fat while holding onto muscle.

So, without further ado, let’s dive in.

The study at hand was conducted to ascertain whether amount of sleep would affect results while dieting. It built upon previous studies showing hormonal disturbances with lack of sleep (which I’ll cover in more detail in a later post), and increases in appetite. So the authors wanted to know whether those changes would actually manifest themselves in meaningful body composition changes when on a controlled, low calorie diet.

Participants

The subjects were 10 overweight (average BMI 27.4) but otherwise healthy people, mostly in their late 30s or early 40s. They were excluded from the study if they were heavy drinkers, smokers, had jacked up sleep habits, had any major abnormalities on a physical, or were habitual heavy caffeine users. In short, they were pretty average, middle aged folks.

The study procedure

For 14 days, participants had to stay in bed for either 8.5 or 5.5 hours per night. At least 3 months later, participants swapped conditions. Food intake was restricted to 90% of resting metabolic rate. Doubly labeled water was used to assess energy expenditure (I won’t go too far afield explaining how it works, but rest assured that doubly labelled water is a VERY good method for assessing energy expenditure accurately). Meals were standardized and weighed to ensure calorie intake was controlled for as tightly as possible. In short, it was a very well-controlled study.

The results

Amount of time the participants actually slept increased or decreased as it was supposed to. Those in bed 8.5 hours per night slept, on average, 7hrs and 25min per night (pretty close to their habitual average before the study of 7.7 hrs/day), and those who were in be 5.5 hours per night slept, on average, 5hrs and 14min.

Energy consumption was darn near identical – about 1450 calories per day. Daily caloric expenditure was also nearly identical – about 2140 calories per day. That’s essentially a 700 calorie daily deficit, which is quite reasonable.

The 5.5 hour group lost 20/80 fat and lean mass. That’s not a typo. Only 1/5 of the weight lost was actually fat. 0.6kg of the 3.0kg total. That’s substantial.

So, in more concrete numbers, the 8.5 hour group lost 2.33x morefat than the 5.5 hour group, and the 5.5 hour group lost 1.6x more lean massthan the 8.5 hour group. If most of us are aiming for body REcomposition (more muscle and less fat), would this be the definition of body DEcomposition? 😉

It doesn’t get much better for the poor sleep deprived subjects from there, either….

Hunger was higher. This was accompanied by greater increases in acylated ghrelin – a hormone that promotes hunger.

Respiratory quotient was higher. That means that for each calorie burned, more of the energy came from carbohydrate, and less of it came from fat.

You need more of thisAnd less of this

Drawbacks

Well, for one, the participants were sedentary. That makes it a little harder to generalize results since resistance exercise helps you retain more muscle while dieting.

Also, at least in the eyes of most people reading this, protein intake was laughably low (about 65g/day). [if you want to find out how much you SHOULD be eating, and how to make the most of it, find out here].

It should be noted that lean mass also includes water. So of the 3kg lost, only about 1.2-1.7kg (2.7-3.8 pounds) of that should come from tissue loss (your body theoretically gets about 3500 calories from a pound of fat, and 2500 from a pound of muscle, so with an overall deficit of 9660 calories on average, some of those 6.6 pounds almost certainly came from water).

With that in mind, let’s do a little rough math. Let’s say both groups lost about 50/50 water/tissue – a fair enough assumption. The 8.5 hour group lost 1.4kg of fat, which means .1kg left over for lean tissue loss (93% fat lost, 7% lean – not too shabby!). The 5.5 hour group lost .6kg of fat, which means .9kg left over for lean tissue loss (40% fat lost, and 60% lean mass. A little better than 20/80, but still pretty dismal).

I’ll admit, that’s just a rough estimate, but it probably gives a little clearer picture of what was actually lost by both groups. The 8.5 hour group probably lost almost all fat and kept their lean tissue quite well, in spite of a 1450 calorie diet, low protein, and no exercise. The 5.5 hour group, no matter how you slice it or dice it, lost a considerable amount of lean tissue, whether that be from muscle, bone, or organs.

If we wanted to go into the weeds of the effects sleep deprivation on cortisol, and cortisol’s effects on water retention, there’s even the potential that the 5.5 hour group was holding onto a little more water, which means even more of their lean mass loss would be muscle… but we’ll be charitable.

Breaking it down

I understand if you’re a little skeptical about how well this would translate to you if you’re eating enough protein and you’re lifting.

Sure, you’d probably do a better job of holding onto lean mass than the 5.5 hour group in this study, BUT we’re probably just talking about the degree to which you stop the bleeding. Maybe instead of 40/60 it would be 60/40 fat/lean. That’s still not painting a rosy picture.

Mechanistically, I have a hard time seeing how improved diet and exercise would mitigate ALL the lean mass loss that comes from losing sleep. There are some well-documented hormonal changes (I’ll talk about those in a later post), a higher RQ means less fat is burned proportional to total energy expenditure so that energy HAS to come from stored glycogen or protein, and acylated ghrelin does some nasty stuff on it’s own. To quote the authors, “Acylated ghrelin has been shown to reduce energy expenditure, stimulate hunger and food intake, promote retention of fat, and increase hepatic glucose production to support the availability of fuel to glucose-dependent tissues.”

Literally the best case scenario with a shift in RQ is this: with adequate protein intake and resistance training, you’re still able to hold onto your lean mass. However, for every calorie you burn, more of it comes from stored glycogen, and less of it comes from stored bodyfat. Less fat burned per calorie burned means you’ll have to diet longer to get lean. More glycogen burned per calorie means you’ll have less energy for your workouts. Elevated acylated ghrelin means you’ll be hungrier. So, if you’re not sleeping enough and doing everything else 100% right, the best possible scenario is that you have to diet for longer, while having crappy workouts and being even hungrier all the time. Sounds like more fun than a barrel of monkeys, right?

The Takeaway

Sleep.

It’s as simple as that. Let’s take it out of the realm of “sleep helps with recovery,” and let’s forget for a moment about the health consequences or fogginess that come from not sleeping. We have concrete evidence that sleep is essential for optimal body composition. Lack of sleep directly makes it harder to burn fat and increases your risk of losing lean mass.

If it’s worth it to you to prioritize training and prioritize nutrition (as seems to be the case for almost everyone), make a point of also prioritizing sleep. Good sleep will magnify the effectiveness of the other two, and bad sleep will be a huge obstacle to your physique goals.

If you’re interested in reading part 2, which is geared more at training implications, here it is.

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About Greg Nuckols

Greg Nuckols has over a decade of experience under the bar, a BS in Exercise and Sports Science, and a Master's in Exercise Physiology. He’s held 3 all-time world records in powerlifting in the 220 and 242 classes.

He’s trained hundreds of athletes and regular folks, both online and in-person. He’s written for many of the major magazines and websites in the fitness industry, including Men’s Health, Men’s Fitness, Muscle & Fitness, Bodybuilding.com, T-Nation, and Schwarzenegger.com. Furthermore, he’s had the opportunity to work with and learn from numerous record holders, champion athletes, and collegiate and professional strength and conditioning coaches through his previous job as Chief Content Director for Juggernaut Training Systems and current full-time work here on Stronger By Science.

His passions are making complex information easily understandable for athletes, coaches, and fitness enthusiasts, helping people reach their strength and fitness goals, and drinking great beer.